<title>Implementation of compression with reversible embedded wavelets</title>

Abstract

Compression with reversible embedded wavelets (CREW) is a unified lossless and lossy continuous-tone still image compression system. 'Reversible' wavelets are nonlinear filters which implement exact-reconstruction systems with minimal precision integer arithmetic. Wavelet coefficients are encoded in a bit-significance embedded order, allowing lossy compression by truncating the compressed data. Lossless coding of wavelet coefficients is unique to CREW. In fact, most of the coded data is created by the lessor significant bits of the coefficients. CREW's context-based coding, called Horizon coding, takes advantage of the spatial and spectral information available in the wavelet domain and adapts well to the lessor significant bits. In applications where the size of an image is large, it is desirable to perform compression in one pass using far less workspace memory than the size of the image. A buffering scheme which allows a one-pass implementation with reasonable memory is described.